U.S. patent application number 11/280402 was filed with the patent office on 2008-04-24 for method and apparatus for optimizing the performance envelope of an engine.
Invention is credited to Daniel Francois.
Application Number | 20080097703 11/280402 |
Document ID | / |
Family ID | 34954778 |
Filed Date | 2008-04-24 |
United States Patent
Application |
20080097703 |
Kind Code |
A1 |
Francois; Daniel |
April 24, 2008 |
Method and apparatus for optimizing the performance envelope of an
engine
Abstract
A method for doing an optimization of the performance envelope
initially authorized for an existing rotorcraft engine (M) to
enable the engine (M), to be used in an optimized performance
envelope that is different from the performance envelope initially
authorized for the engine, is remarquable in that this optimization
is compensated by modifying the total service life of the engine
(M).
Inventors: |
Francois; Daniel; (Salon De
Provence, FR) |
Correspondence
Address: |
YOUNG & THOMPSON
745 SOUTH 23RD STREET, 2ND FLOOR
ARLINGTON
VA
22202
US
|
Family ID: |
34954778 |
Appl. No.: |
11/280402 |
Filed: |
November 17, 2005 |
Current U.S.
Class: |
702/34 ; 700/1;
700/28; 702/1; 702/127; 702/182; 702/187; 702/189; 702/32;
702/33 |
Current CPC
Class: |
F02C 9/00 20130101; F05D
2270/303 20130101; F05D 2270/053 20130101; F02C 9/28 20130101; F05D
2270/11 20130101 |
Class at
Publication: |
702/34 ; 702/1;
702/33; 702/127; 702/182; 702/187; 702/189; 700/1; 700/28;
702/32 |
International
Class: |
G06F 19/00 20060101
G06F019/00; G06F 17/40 20060101 G06F017/40 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 25, 2004 |
FR |
04 12532 |
Claims
1. A method for doing an optimization of the performance envelope
initially authorized for an existing rotorcraft engine (M) to
enable said engine (M) to be used in an optimized performance
envelope that is different from said performance envelope initially
authorized for said engine (M), during which method said
optimization is compensated by a change to the total service life
of said engine.
2. A method according to claim 1, characterized in that, for said
initially-authorized performance envelope comprising at least one
operating rating corresponding to a given power level (PMC, PMD,
PIU, PMU, PSU) and to a given utilization time, said optimization
is performed by modifying said power (PMC, PMD, PIU, PMU, PSU) of
said rating.
3. A method according to claim 1, characterized in that, for said
initially-authorized performance envelope comprising at least one
operating rating corresponding to a given power (PMC, PMD, PIU,
PMU, PSU) and a given utilization time, said optimization is
performed by modifying said utilization time of said rating.
4. A method according to claim 1, characterized by the following
steps: calculating in real time the instantaneous damage of said
engine (M); from said instantaneous damage, deducing the real
damage (ER1, ER2, ER3) of said engine since its most recent
overhaul; and removing said engine (M) from the rotorcraft in order
to overhaul it as soon as a first condition is satisfied whereby
said real damage (ER1, ER2, ER2) is at its maximum amount.
5. A method according to claim 1, characterized by the following
steps: calculating in real time the instantaneous damage of said
engine; from said instantaneous damage, deducing the real damage
(ER1, ER2, ER3) of said engine (M) since its most recent overhaul;
determining whether a first condition is satisfied whereby said
real damage (ER1, ER2, ER3) is at its maximum amount; measuring in
real time the number of flying hours performed by said engine (M)
since its most recent overhaul; determining whether a second
condition is satisfied whereby said number of flying hours is equal
to the time between overhauls (TBO) of said engine (M); and
removing said engine (M) from the rotorcraft to overhaul it as soon
as said first or said second condition is satisfied.
6. A method according to claim 4, characterized in that said
instantaneous damage is calculated from a deterioration coefficient
(K) obtained from a curve (CO) determining said deterioration
coefficient (K) as a function of the value of a monitored parameter
of said engine (M).
7. A method according to claim 6, characterized in that said engine
(M) is provided with a high pressure turbine and said monitored
parameter is the turbine entry temperature (TET) of the gas at the
inlet to said high pressure turbine.
8. A method according to claim 6, characterized in that said engine
(M) is provided with a free turbine, and said monitored parameter
is the temperature (T4) of the gas at the inlet to the free
turbine.
9. A method according to claim 5, characterized in that said
instantaneous damage is calculated from a deterioration coefficient
(K) obtained from a curve (CO) determining said deterioration
coefficient (K) as a function of the value of a monitored parameter
of said engine (M).
10. A method according to claim 9, characterized in that said
engine (M) is provided with a high pressure turbine and said
monitored parameter is the turbine entry temperature (TET) of the
gas at the inlet to said high pressure turbine.
11. A method according to claim 9, characterized in that said
engine (M) is provided with a free turbine, and said monitored
parameter is the temperature (T4) of the gas at the inlet to the
free turbine.
12. Apparatus for a rotorcraft having at least one engine (M), the
apparatus implementing the method according to any preceding claim
and being provided with management means (G) for measuring in real
time said number of flying hours of said engine, the apparatus
being characterized in that it comprises a meter (C) for
calculating the real damage (ER1, ER2, ER3) of said engine (M).
13. Apparatus according to claim 12, characterized in that said
meter (C) includes a calculator (C2).
14. Apparatus according to claim 12, characterized in that said
meter (C) includes a clock (C1).
15. Apparatus according to claim 9, characterized in that said
meter (C) is integrated in said management member (G).
16. Apparatus according to claim 9, characterized in that it
includes display means (V) for informing the pilot of said
rotorcraft about said real damage (ER1, ER2, ER3) suffered by said
engine since its most recent overhaul.
17. Apparatus according to claim 16, characterized in that said
display means (V) displays the number of flying hours performed by
said engine since its most recent overhaul.
Description
[0001] The present invention relates to a method and to apparatus
for using a rotorcraft turboshaft engine in an optimized
performance envelope that is different from the performance
envelope initially authorized for the engine.
[0002] Most rotorcraft presently being built have one or two free
turbine engines. Power is taken from a low-pressure turbine
referred to as a "free" turbine, which is mechanically independent
of the compressor assembly and the high-pressure stage of the
engine, which stage comprises a high-pressure turbine in
particular. The free turbine of an engine generally rotates at a
speed in the range 20,000 revolutions per minute (rpm) to 50,000
rpm, so a stepdown gearbox is needed for its connection to the main
rotor of the rotorcraft, since its speed of rotation lies
substantially in the range 200 rpm to 400 rpm: this is known as the
main transmission gearbox.
[0003] The temperature limitations of an engine and the torque
limitations of a main gearbox serve to define a performance
envelope covering two normal utilization ratings for an engine
arranged on a single- or twin-engined rotorcraft; [0004] takeoff
rating corresponding to a level of torque for the gearbox and to a
level of temperature for the engine that can be accepted for a
limited length of time without significant degradation: this is
known as maximum takeoff power (PMD) and can be used for five
minutes; and [0005] maximum continuous rating during which, at no
time, are the capabilities of the gearbox exceeded or the
capabilities of the engine exceeding relating to the maximum
temperature that can be accepted continuously ahead of the high
pressure blades of the first stage of the turbine: this is maximum
continuous power (PMC) and it can be used without time limit,
corresponding to about 90% of PMD.
[0006] On a twin-engined rotorcraft, the performance envelope also
covers emergency ratings, for use only with one engine inoperative
: [0007] the first emergency rating during which the capabilities
of the inlet stages of the gearbox and the temperature capabilities
of the engine are used to the maximum: this rating can be used for
a maximum of thirty consecutive seconds, and on three occasions in
any one flight, it is equal to about 112% to 120% of PMD and is
referred to in the art as super-emergency power (PSU).
[0008] The use of PSU requires the engine to be removed and
overhauled; [0009] the second emergency rating in which the
capabilities of the inlet stages of the gearbox and the temperature
capabilities of the engine are used to a very great extent: this
rating is equal to approximately 105% to 110% of PMD, it can be
used for a maximum of two consecutive minutes, and it is referred
to as maximum emergency power (PMU) [0010] the third emergency
rating during which the capabilities of the inlet stages of the
gearbox and the temperature capabilities of the engine are used
without inflicting damage: this is the intermediate emergency power
equal to the PMD that can be used with one engine inoperative and
can be used for the remainder of the flight, being referred to as
PIU.
[0011] Consequently, the temperature and mechanical constraints,
and above all the phenomenon of turbine blade creep, lead to the
engine being degraded to a greater or lesser extent depending on
the rating. To guarantee safety in flight and to obtain high
performance, it is therefore essential to determine the maximum
amount of damage that is acceptable for an engine.
[0012] Thereafter, the total service life of the engine is
evaluated. In practice, this reduces to defining a maximum number
of flying hours that the engine can perform between overhauls (or
since its first use, depending on circumstances), and is referred
to as time between overhauls (TBO). Once TBO has been reached, the
engine is removed and overhauled.
[0013] For convenience in the text below, the term "most recent
overhaul of the engine" is used to designate either first use of
the engine or else the genuine most recent overhaul thereof.
[0014] Furthermore, in order for a rotorcraft to obtain
authorization to fly in any given country, it is required that the
performance envelope and the TBO of the engine(s) of the rotorcraft
be certified by the official services in the country in question
for a precise utilization spectrum. Such authorization is therefore
achieved only after complete certification testing that is very
expensive.
[0015] Since such complete certification tests of an engine are
performed specifically to justify a performance envelope associated
with a TBO, it is not possible to use the engine with a performance
envelope different from the initially-authorized performance
envelope, without performing new complete certification tests that
are very expensive.
[0016] By way of example, it is found that the performance envelope
of the type described above, associated with a TBO of about 2500
hours, corresponds to a utilization spectrum of a type that matches
most civil applications. Nevertheless, for military applications or
for certain particular missions, e.g. a rescue mission requiring
winching into a helicopter, such an envelope can be insufficient.
While on the contrary, in other situations, the envelope might be
overdimensioned.
[0017] To remedy this problem, one solution would be to manufacture
different engines dedicated to specific applications for a given
rotorcraft airframe. However, given the cost of development,
certification, and integration, that solution can be seen to be
unsatisfactory. Production levels must be high in order to recover
adequately the investment involved. That goes against the desired
principle whereby a special performance engine is used on an
existing rotorcraft in order to satisfy a particular need, which by
its very nature implies short production runs.
[0018] Under such conditions, an object of the present invention is
to provide a method and apparatus for optimizing the performance
envelope initially authorized for an existing rotorcraft engine by
performing additional tests only, and not complete testing.
[0019] It then becomes possible to use an existing rotorcraft that
is intended for specific applications with an engine that was not
initially designed for that purpose. Thus, the helicopter
manufacturer can avoid the very large development costs associated
with a new engine and can optimize the capabilities of an engine
that has already been certified and proven, e.g. in civilian
use.
[0020] According to the invention, a method for doing an
optimization of the performance envelope initially authorized for
an existing rotorcraft engine to enable said engine to be used in
an optimized performance envelope that is different from said
performance envelope initially authorized for said engine, is
remarquable in that this optimization is compensated by modifying
the total service life of said engine.
[0021] In addition, since the initially-authorized performance
envelope covers at least one operating rating corresponding to a
given power level and to a given utilization time, optimization
consists in changing the power level and/or the utilization time
for said rating.
[0022] Thereafter, the TBO associated with the initially-authorized
performance envelope is no longer genuinely representative of the
total service life of the engine. However, determining a new TBO
for association in the future with the optimized performance
envelope would be penalizing and unprofitable for the manufacturer
from a financial point of view, since it would then be necessary to
carry out certification testing again.
[0023] Thus, according to the invention, monitoring means are
installed associated with calculating the real damage to the engine
since the most recent overhaul. Compared with the
initially-authorized performance envelope, use of the optimized
performance envelope then takes place with equivalent safety levels
since the real damage to the engine since its most recent overhaul
is computed and monitored in real time during the flights performed
using the engine of a rotorcraft.
[0024] To do this, in a first implementation, the following steps
are performed: [0025] calculating in real time instantaneous damage
of said engine; [0026] deducing from the instantaneous damage the
real damage suffered by the engine since its most recent overhaul;
and [0027] removing the engine for overhaul as soon as a first
condition is satisfied indicating that the real damage is at its
maximum, i.e. is equal to 1.
[0028] Consequently, this method enables the initially-authorized
performance envelope to be optimized by modifying the total service
life of the engine.
[0029] If the optimization consists in increasing performance, i.e.
increasing power and/or the length of time a rating can be used or
even creating a new rating, for example, then the consequence of
implementing the optimized performance envelope is greater
degradation of the engine compared with implementing the
initially-authorized envelope. The total service life is no longer
strictly equal to the TBO but to a duration that will be shorter,
and that will be reached when the real damage reaches its maximum.
Thus, the total service life becomes shorter than the TBO.
[0030] Nevertheless, if the engine is used in application of the
initially authorized performance envelope, then its total service
life will be equal to the TBO, since its real damage will reach its
maximum at that time.
[0031] Similarly, if optimization consists in reducing the
performance of the engine, then the real damage will not be at its
maximum when the TBO is reached, thereby enabling the total service
life of the engine to be increased.
[0032] In a second implementation seeking to increase safety, the
TBO is retained for determining whether the total service life of
the engine has been used up. Thus the following steps are
performed: [0033] calculating in real time the instantaneous damage
of the engine; [0034] from the instantaneous damage, deducing the
real damage of the engine since its most recent overhaul; [0035]
determining whether a first condition is satisfied whereby the real
damage is at its maximum; [0036] measuring in real time the number
of flying hours performed by the engine since its most recent
overhaul; [0037] determining whether a second condition is
satisfied whereby said number of flying hours is equal to the
engine's TBO; and [0038] removing the engine from the rotorcraft in
order to overhaul it as soon as the first or the second condition
is satisfied.
[0039] Advantageously, the instantaneous damage is evaluated from a
deterioration coefficient obtained using a curve or any other
similar means, such as a data table for example, that determines
said deterioration coefficient as a function of the value of a
monitored parameter of the engine.
[0040] In addition, for an engine provided with a high-pressure
turbine upstream from a free turbine, the monitored parameter is
the turbine entry temperature (TET), i.e. the temperature of the
gas at the inlet to the high-pressure turbine.
[0041] The blades of the high-pressure turbine of the engine are
subjected to centrifugal force and to the TET. Above a certain
threshold, the material from which the blades are made begins to
"creep", thereby lengthening the blades. This causes them to come
into contact with the casing of the high-pressure turbine and thus
be degraded. The TET is thus directly associated with engine
degradation.
[0042] Nevertheless, since TET is very difficult to measure given
its relatively non-uniform nature, the monitored parameter is
preferably the temperature known as T4 in the art, i.e. the
temperature of the gas at the inlet to the free turbine. This
temperature is a good image of the TET and it is therefore likewise
representative of engine degradation.
[0043] The present invention also provides apparatus for a
rotorcraft provided with at least one engine and implementing the
method of the invention. The apparatus is provided with management
means for measuring in real time the number of flying hours
performed by the engine of the rotorcraft since its most recent
overhaul.
[0044] In addition, it advantageously includes a meter provided
with a clock and a calculator for calculating the real damage of
the engine.
[0045] The meter may be independent of or integrated in the
management means.
[0046] Finally, display means are arranged in the rotorcraft
cockpit so that the pilot is aware of the real damage and
optionally of the number of flying hours that have elapsed since
the most recent overhaul of the engine.
[0047] The apparatus of the invention thus makes it possible to
optimize the performance envelope of the engine of a rotorcraft.
Consequently there is no need to perform complete testing in order
to obtain flying authorization for the rotorcraft as modified in
this way. Simple additional tests suffice to demonstrate that the
engine can accept the new ratings and/or the new power levels or
utilization durations for existing ratings, and to establish the
relationship on which the calculation of instantaneous damage is
based. The cost of such additional testing comes to about 10% of
the cost of developing a new engine, thus enabling the manufacturer
to achieve a considerable saving.
[0048] The invention and its advantages appear in greater detail
from the following description of a preferred implementation given
without any limiting character and with reference to the
accompanying drawing, in which:
[0049] FIG. 1 is a block diagram of apparatus of the invention;
[0050] FIG. 2 is a graph showing the curve for determining the
deterioration coefficient; and
[0051] FIG. 3 is a graph for explaining how real damage is
calculated.
[0052] FIG. 1 is a block diagram of the apparatus D of the
invention.
[0053] It comprises an engine M arranged on a twin-engined
rotorcraft (not shown in FIG. 1) of known type. Initially, the
engine M is certified to operate in a conventional civilian
utilization spectrum. The performance envelope initially authorized
for the engine M thus covers the various ratings mentioned above,
i.e. the normal ratings and the first, second, and third
super-contingency ratings.
[0054] In order to perform a rescue mission, it is often necessary
to use a heavily equipped rotorcraft capable of having a long
radius of action, or even capable of being refueled in flight. Such
a rotorcraft thus presents high tonnage, thus requiring a takeoff
rating using a level of power that is greater than the present
power PMD.
[0055] In addition, in order to guarantee safety of a twin-engined
rotorcraft while winching, it is preferable in emergency mode for
the first emergency rating to be used continuously for a length of
time that is greater than 30 seconds.
[0056] For a specific utilization spectrum, it can thus be
necessary to define an optimized performance envelope for an engine
that is different from the envelope initially authorized
therefor.
[0057] By way of example, for a twin-engined rotorcraft, the
following new normal ratings and/or new durations of utilization
are obtained for each engine: [0058] optimized takeoff rating
having takeoff power PMD' that is equivalent to the PMD but that
can be used for 30 minutes; [0059] maximum continuous rating having
a power PMC that is equal to 90% of PMD and that can be used
without limit on duration; and [0060] an exceptional rating having
an exceptional twin-engined power level, referred to as PEB for
convenience, equal to 107% of PMD and usable for 5 minutes.
[0061] Similarly, when one of the two engines of the twin-engined
rotorcraft is inoperative, the emergency ratings and their
utilization times become, for example: [0062] third emergency
rating usable without limitation on duration; [0063] optimized
second emergency rating of power PMU' that is equivalent to PMU but
usable for 15 minutes; and [0064] optimized first emergency rating
of power PSU' that is equivalent to PSU but usable for 2 minutes
plus two periods of 30 seconds.
[0065] The optimized performance envelope concerning these new
ratings is given purely by way of example and could naturally be
different depending on requirements.
[0066] Given this optimization, the engine runs the risk of
degrading more quickly. The TBO as measured by management means G
and normally representative of engine damage might now be
over-evaluated. To avoid particularly onerous certification costs,
the apparatus D includes a meter C for determining accurately the
real damage to the engine.
[0067] The meter C has a calculator C1 and a clock C2 enabling it
to determine the real amount of engine's damage by using a method
that is explained below with reference to FIGS. 2 and 3.
[0068] In a first implementation, the engine M is removed for
overhaul in the event of a first condition being satisfied,
indicating that the real damage has reached its maximum.
[0069] Thus, since this optimized performance envelope inflicts
more damage on the engine M than does the initially-authorized
performance envelope, the total service life of the engine M is
decreased since the real damage will reach its maximum level before
the TBO is reached. Optimization of the initially-authorized
performance envelope is thus compensated by a change, specifically
a reduction, in the total service life of the engine M.
[0070] In a second embodiment, a second overhaul condition is
established. It consists in verifying whether the number of flying
hours performed by the engine M is equal to TBO.
[0071] Under these conditions, the engine M is overhauled as soon
as either the first or the second condition is satisfied. Taking
the second condition into account makes it possible to increase
safety by ensuring redundancy for the monitoring means concerned
with degradation of the engine M.
[0072] In addition, the apparatus of the invention includes display
means V provided with a screen E, e.g. arranged in the cockpit of
the rotorcraft. It displays the number of flying hours performed by
the engine and also its real damage. Naturally, these two
measurements are set to zero when the engine is used for the first
time or after it has been overhauled, with this moment being
referred to as the "most recent overhaul" in the present
specification.
[0073] FIG. 2 is a graph plotting a curve CO that determines a
deterioration coefficient K needed for calculating real damage. The
value of a monitored parameter of the engine is plotted along the
abscissa and the corresponding value of the deterioration
coefficient K is plotted up the ordinate.
[0074] Preferably, for an engine including a free turbine, the
monitored parameter is the temperature T4 of the gas at the inlet
to the free turbine. This temperature T4 is indeed representative
of the state of the engine since the main cause of damage to the
engine is a temperature that is too high. The greater the
temperature rise of the engine, the more it is degraded. This
observation also explains the exponential shape of the curve
CO.
[0075] FIG. 3 is a graph for explaining how real damage is
calculated, with time being plotted along the abscissa and engine
power up the ordinate.
[0076] At instant t1, the real damage is equal to ER1.
[0077] Under the action of the pilot, for example, the engine then
changes from power P1 to power P2, corresponding to a T4
temperature of value T4.sub.1. From the curve CO, or from any other
equivalent means, the calculator C2 of the meter C deduces from
this temperature the value K1 for the deterioration coefficient K
and calculates the instantaneous damage by dividing K1 by TBO.
[0078] The calculator C2 then makes use of information from the
clock C1 to establish the duration D1 during which the engine is at
power P2 and consequently at temperature T4.sub.1 at the inlet to
its free turbine.
[0079] In order to determine the real damage ER2 at instant t2, and
thus at the end of the duration D1, the calculator C2 multiplies
the instantaneous damage by the duration D1 and adds the product to
the value ER1 for the real damage at instant t1.
[0080] Similarly, with the engine delivering a power P3 from
instant t2 to instant t3, for a duration D2 during which the
monitored temperature has a value T4.sub.2, the calculator C2
determines the real damage ER3 at instant t3 using the following
relationship:
ER 3 = ER 2 + K 2 TBO .times. D 2 ##EQU00001##
[0081] In the first implementation, if the real damage ER3 at
instant t3 is at the maximum, i.e. if it is equal to 1, then it
will be necessary to remove the engine from the rotorcraft in order
to overhaul it.
[0082] Nevertheless, in the second implementation, even if the real
damage has not yet reached its maximum, an overhaul will be
undertaken in the event of the number of flying hours of the engine
reaching its TBO.
[0083] In addition, the apparatus D further includes a plurality of
alarms that are operated by the management means G or by means not
shown in the figures. These alarms are intended specifically to
warn the pilot that: [0084] the length of utilization time for the
rating in use has expired or is about to expire; [0085] the TBO of
an engine has been reached or is about to be reached; and [0086]
the real damage of an engine is at its maximum, or is about to
reach its maximum.
[0087] Thus, as a function of the information presented, the
rotorcraft pilot can select an operating rating that is adapted to
the situation.
[0088] Finally, in order to simplify the apparatus D and reduce its
size, in a first variant of the invention, the meter C is
integrated in the management means G.
[0089] Similarly, in a second variant, the meter C is integrated in
the display means V.
[0090] Naturally, the present invention can be implemented in a
wide variety of ways. Although one implementation is described
above, it will naturally be understood that it is not conceivable
to identify all possible implementations exhaustively. It is
naturally possible to envisage replacing any of the means described
by equivalent means without thereby going beyond the ambit of the
present invention.
* * * * *